The present invention relates to a device that supports a loop of optical fiber such that the loop may be used to test fiber optic-related equipment.
Optical fibers were introduced in the early 1970s. Since that time, their use has expanded into numerous settings. Additionally, a number of different forms of optical fibers have appeared. The principle division is between single-mode fibers and multi-mode fibers, with multi-mode fibers being further divided into graded index multi-mode and step-index multi-mode fibers. As understood in the fiber optic industry, a xe2x80x9cmodexe2x80x9d is a transverse pattern of energy propagating at a specific velocity through the fiber.
Multi-mode fibers, as the name suggests, support a number of modes. Multi-mode fibers offer the advantages of being able to be coupled to incoherent light sources and having a wider tolerance for alignment with these light sources. Multi-mode fibers may be connected and spliced one to another with a fair amount of latitude. Additionally, multi-mode fibers are generally forgiving when it comes to losses induced by bends in the fiber. That is, the fiber may bend fairly substantially without worry about losses induced by the bend. Two disadvantages of multi-mode fibers are intermodal dispersion wherein different modes may travel at different velocities and relatively high attenuation.
Single mode fibers, in contrast, only support a single mode, namely the HE11 mode. Single-mode fibers do not suffer from internodal dispersion, are generally considered to have higher bandwidth capabilities than multi-mode fibers, and are relatively insensitive to losses induced by local lateral microdisplacements of the fiber from a mean axis (microbendingxe2x80x94bends on the order of the size of the core of the fiber). However, single-mode fibers are more susceptible to losses generated by macroscopic bending. As the radius of curvature decreases, losses within the fiber increase. Further, greater care when splicing single-mode fibers is required.
Those who use fibers are greatly concerned with losses because loss dictates how far a signal will propagate within the fiber and still be usable. While amplifiers may counteract losses, each amplifier in a system increases costs and requires additional connective infrastructure. Knowledge of a loss profile of a fiber is extremely helpful when designing fiber based systems so that appropriate hardware or signal processing is used to compensate for the known losses.
In 1998, SIECOR introduced a duplex connector to replace the traditional SC type connector. This new connector, known as the MT-RJ, is approximately the size of a phone plug, allowing connector density within fiber systems to double effectively over the old SC type connectors and achieve densities equal to, or in some cases better than, copper-based systems. The MT-RJ has rapidly become the industry standard for fiber optic systems. An additional feature of the MT-RJ connector is its ability to be used with both single-mode and multi-mode fibers.
As a result of the rapid acceptance of the MT-RJ, new devices within fiber optic systems are now being equipped with MT-RJ female receptacles to mate with the male end of the MT-RJ. Manufacturers of such devices include CISCO, 3COM, and others within the telecommunications industry. Examples of such devices include Optical Time Domain Reflectometers (OTDRs), routers, optical transceivers, optical amplifiers, and the like. Specific examples include the CATALYST 8500 family of non-blocking multiservice switch routers from CISCO, the CFX-1433M 100Mbps Fast Ethernet Hub from Canary Communications, and 12RJ-3200A HP ADVANCESTACK 10base-T Hubs. However, these devices must frequently be tested to see if they are functioning properly. This is especially important before shipping to a consumer, as the companies producing these devices do not want to ship defective products. Additionally, it may be desirable to test these devices after installation to verify that they are not the source of system failure.
SIECOR has introduced a device coupled to an MT-RJ connector that allows testing of system devices using multi-mode fibers. However, this device has a flexible fiber element and is inappropriate for use with a single-mode fiber. In particular, this device is especially susceptible to drooping as a result of temperature increases. This droop induced bending is acceptable in a multi-mode fiber, but not for a comparable single-mode fiber. As a result, there is still a need for a device that utilizes a single-mode fiber to test the functionality of fiber optic system devices.
The shortcomings of the prior art are addressed by providing a rigid support that holds a single-mode fiber in a position with a relatively constant or repeatable loss profile and further is adapted to connect to an MT-RJ connector. An exemplary embodiment of the present invention comprises a generally planar, rigid, plastic housing. The housing may be approximately three and a half (3.625) inches long and have a slotted first end. The slot gives access to a cavity extending substantially the length of the housing, in effect forming a sleeve. The slot includes an arcuate center area sized to accommodate the standard protuberance on the end of a standard MT-RJ connector. In use, a single-mode fiber or filament is secured to the MT-RJ and then slipped into the slot. The protuberance on the MT-RJ may be secured to the housing to form the testing device. In essence, the support acts like a sleeve positioned over the filament that is secured to the MT-RJ. The loss characteristics of the testing device may then be determined empirically, and the testing device labeled with appropriate indicia indicative of the empirically determined loss characteristic. Subsequently, the testing device may be used repeatedly to verify the functionality of other fiber optic system devices. The housing holds the filament loop such that the loss characteristic of the loop does not change between uses and likewise is not susceptible to bending such as may occur in the SIECOR multi-mode testing unit.